Metal components are used in a wide variety of industrial applications, under a diverse set of operating conditions. In many cases, the components are provided with coatings which impart various characteristics. As one example, the various components of turbine engines are often coated with thermal barrier coatings, to effectively increase the temperature at which they can operate. Other examples of articles which require some sort of protective coating include pistons used in internal combustion engines and other types of machines.
Wear-resistant coatings (often referred to as “wear coatings”) are frequently used on turbine engine components, such as nozzle wear pads and dovetail interlocks. Such coatings provide protection in areas where components may rub against each other, since the rubbing, especially high frequency rubbing, can damage the part. A specific type of wear is referred to as “fretting.” Fretting can often result from very small movements or vibrations at the juncture between mating components, for example, in the compressor and/or fan section of gas turbine engines. For example, fretting can occur in regions where fan or compressor blades are joined to a rotor or rotating disc. This type of wear results in premature repair or replacement of one or more of the affected components. Various alloys, such as those based on nickel or cobalt, are susceptible to fretting and other modes of wear. Many titanium alloys have especially poor anti-fretting characteristics.
Specifically, compressor dovetails in industrial gas turbines can be subject to contact stress, fretting motion, corrosive environments, and combinations thereof. Such factors can decrease the useful life of the dovetails and/or decrease duration between repairs.
Known processes repair and/or protect dovetails by applying dry film lubricating systems having coarse lubricating particles embedded in an epoxy binder or a spray baked inorganic binder. Such dry film lubricating systems have limited life due to poor integrity of low temperature cured binders, large lubricating particles that can be pulled out, leading to coating wear and direct exposure to base metal; this also can lead to limited corrosion protection. In coatings with an undesirable degree of wear resistance, pitting damage can occur due to crevice corrosion either because the coatings are not protective enough or uncoated components, such as blades are used. Such damage can result in accrued fretting fatigue damage that can result from cracks being nucleated and propagated leading to damage to an overall system such as a gas turbine.
Other known processes have failed to provide a desirable degree of wear resistance, and lubrication.
A coating composition, a process of applying a coating, and a process of forming a coating composition not suffering from one or more of the above drawbacks would be desirable in the art.